This invention relates to an improvement in an insulating spacer for gas insulated equipment.
Heretofore, a disk-shaped or circular-cone-shaped insulating spacer for gas insulated equipment has been secured to a metal sheath according to a method in which the periphery of the spacer is held by a flange formed on the metal sheath. FIG. 1 is a longitudinal sectional view illustrating a method of securing a conventional disk-shaped insulating spacer to a metal sheath. In FIG. 1, reference numeral 1 designates the disk-shaped insulating spacer; element 2, the sheath to which the spacer 1 is secured; and element 3, a conductor. The internal space defined by the conductor 3 and the metal sheath 2 is filled with SF.sub.6 gas 4 having excellent insulation characteristics.
FIG. 2 is a longitudinal sectional view illustrating a method of securing a conventional circular-cone-shaped insulating spacer to a metal sheath. In FIGS. 1 and 2, like components are designated by like reference numerals. More specifically, in FIG. 2, reference numeral 1 designates the circular-cone-shaped insulating spacer; the metal sheath having a flange surrounding the spacer to which the spacer is secured to is element 2; and numeral 3 designates a conductor. The space between the conductor 3 and the metal sheath 2 is filled with SF.sub.6 gas 4. FIG. 3 is an enlarged view showing the mounting part of the insulating spacer 1, through which the insulating spacer 1 is secured to the metal sheath 2, in the case of FIG. 1 or 2. In FIG. 3, those components which have been previously described with reference to FIGS. 1 and 2 are therefore similarly numbered. When the flange-shaped part of the metal sheath 2 holds the periphery of the spacer 1, the spacer 1 is brought into contact with the metal sheath through opposed end portions having arcs R1 which are formed by opposed bends of the flange-shaped portion. The distribution of electric field strength at the flange-shaped portion is shown in FIG. 4. As shown in FIG. 4, the electric field strength is not uniform at the flange-shaped portion, and the electric field strength (hereinafter referred to as "stress", when applicable) is a maximum at the opposed end portions R1 of the arcs. Accordingly, when the insulating spacer 1 is brought into contact with the sheath 2 at the opposed end portions of the arcs, the stress is significantly increased. As a result, the contact region where the spacer 1 and the sheath 2 are in contact with each other becomes electrically weak. Hence, the flashover voltage of the spacer is greatly decreased, and the insulating characteristic is degraded.